Paper tray with leaf spring

ABSTRACT

A paper bin assembly including a movable bottom tray for holding a stack of print receiving material, such as paper. The assembly is designed for insertion into a machine using sheets of paper, such as a copier or printer. A leaf spring is used to move the tray upwardly to keep the top sheet of the stack in position for being fed from the stack by a paper feeding mechanism. As sheets are fed from the stack, the spring continues to provide the top sheet in position, and continues to provide a correct normal force between the paper feeding mechanism and the top sheet. This is accomplished over a wide range of paper size and density by affording an adjustment mechanism to vary the spring rate. The adjustment mechanism involves a movable spring support member which moves in one direction relative to a fixed spring support member, and by providing an offset in a second dimension between the two spring support members.

This invention relates to paper handling devices and, more particularly,to paper bins for use in feeding sheets of paper serially into machines,such as a copier or printer.

BACKGROUND OF THE INVENTION

In machines, such as copiers or printers, paper or other print-receivingmaterial is held in a paper bin and fed, one sheet at a time, into themachine. Frequently, paper bins are used which hold a large amount ofpaper; for example, a stack of 500 sheets or more. To reload a bin, apaper tray is usually slideably removed from operating engagement withinthe machine, a stack of paper is placed onto the tray and the tray isreturned to operating position within the machine. Normally, the stackof paper is placed on a tray which is mounted on powered elevatormechanisms which move the loaded tray upwardly so that the top sheet onthe tray contacts paper feed rolls positioned above the paper stack.Arrangements of this kind, while suitable for more expensive high-volumemachines, are not suitable for low cost slower speed desk-top machines.Usually, the low cost machines contain paper cassettes which may hold,for example, a stack of 25 or 50 sheets. In arrangements of this kind,the stack of paper is placed in the cassette on a tray which is springbiased upwardly so that the top sheet on the tray contacts paper feedrolls positioned above the cassette. In that manner, expensive poweredelevator arrangements are avoided.

It is an object of this invention to provide a spring-biased traycapable of holding a large amount of paper (for example, 500 sheets ormore) so that a paper bin of considerable size can be utilized on a lowcost copier or printer.

It is another object of this invention to provide a spring mechanism foruse with a paper tray which is easily adjustable for different weightand sizes of paper.

It is still another object of this invention to provide a paper traywith a leaf spring having an adjustable spring rate so that the contactforce between the paper and the feed roll is maintained fairly constantas the number of sheets in the tray decreases from a large number, suchas 500, to 0.

It is another object of this invention to provide a paper tray with alift spring rate which is adjustable to provide a proper feed rollcontact force regardless of the weight and size of the paper.

The objects of the instant invention have not been met in the prior art.U.S. Pat. No. 4,337,935 shows a typical paper cassette in which a coilspring lifts a paper tray so that contact may be made with a feed roll.Such a device is useful in paper cassettes, but is not capable ofhandling a large number of sheets.

U.S. Pat. No. 4,350,328 shows a sheet-feeding apparatus in which apivotally disposed tray is urged upwardly by an arm which is pivotallymounted and biased by a coil spring.

U.S Pat. No. 4,765,604 shows a paper tray upwardly biased by an armwhich is pulled upwardly by a coil spring.

SUMMARY OF THE INVENTION

This invention relates to a sheet-holding mechanism in which a movabletray is located within a paper holding bin, and which is biased upwardlyby a leaf spring mechanism whose spring rate is adjustable. In thatmanner, the top sheet of a stack of paper situated on the paper tray isbrought into position for being fed by a feed roll into a processingmachine. Adjustment of the leaf spring rate enables the mechanism tomaintain correct normal force between the feed roll and the top sheet ofpaper over a wide range of paper weight and throughout the feedingoperation regardless of the number of sheets remaining in the tray.Adjustment is accomplished by providing a movable support member for theleaf spring such that the spring rate is changed as the movable supportmember is moved. As the spring rate is reduced, the leaf spring isenabled to provide an increased deflection. In that manner, the leafspring force is varied linearly with relatively small angles ofdeflection. The mechanism is provided with an offset between the heightof the movable support member and a fixed leaf spring support member sothat the leaf spring will exhibit a constant no-paper-load force on thepaper tray regardless of the position of the movable support member. Inthat manner, an adjustment range is provided to accommodate a range ofsizes and densities of paper so that a proper normal force between thetop sheet and the feed roll can be maintained regardless of the numberof sheets in the bin, and regardless of the density and size of thepaper in the bin within the range provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned objects and other features and objects of thisinvention, and the manner of attaining them, will become more apparent,and the invention itself will best be understood by reference to thefollowing description of embodiments of the invention taken inconjunction with the accompanying drawings, the description of whichfollows.

FIG. 1 shows a copier or printer machine with a paper bin holding atleast 500 sheets.

FIG. 2 shows an exploded view of the parts which comprise the paper binof the instant invention for use in the machine of FIG. 1.

FIG. 3 is a schematic diagram of the manner in which the movable leafspring support is caused to travel.

FIG. 4 is a schematic diagram of the paper feed mechanism of the instantinvention.

FIG. 5 is a schematic representation of the leaf spring arrangement ofthe instant invention.

FIG. 6 is a graphical representation of the variation in spring forcewith the number of sheets contained in the paper tray.

FIG. 7 is a graphical representation of the variation in spring forcewith variation in the position of the movable leaf spring support.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a printing or copier machine of the type in which theinstant invention can be employed. A paper bin assembly 10 is shown outof the machine so that sheets of print-receiving material, usuallypaper, can be loaded into the assembly.

FIG. 2 is an exploded view of paper bin assembly 10 showing the partsthereof. A bottom cover 11 contains a notch 12 providing access for amachine operator to the side of a thumb wheel 13. The thumb wheel 13drives a thumb wheel gear 14 which contacts a second gear 15 which, inturn, drives a rack 16. Rack 16 is directly connected to a movablespring support member 17. Movable spring support member 17 carries ashaft 45 with rollers 43 and 44 which contact the underside of leafspring 18. Leaf spring 18 is fixedly supported at end 19 by a stud 20and a set screw 21. A roller 22 is mounted in end 23 of leaf spring 18.The underside of paper tray 24 rests on top of roller 22. Paper tray 24is also pivotally mounted through ears 25 which are held by paper traybase 26.

Other elements of the paper bin assembly 10 include a preload spring 27which is connected to the tray base 26 at one end, and to a preload arm28 on the other end. Preload arm 28 is pivotally mounted together with acorner buckler arm 29. A corner buckler pointer 30 is mounted on thecorner buckler arm 29. FIG. 2 also shows an adjustable paper stop 31, atray cover 32, an adjustable paper guide 33, and a support plate 60which covers the corner buckler arm 29 and preload arm 28 so that papermoves by them in an unimpeded fashion.

FIG. 3 shows the manner in which the leaf spring movable support member17 is moved by the thumb wheel 13. A notch 12 is provided in the bottomcover 11 and in the paper tray base 26 (not shown in FIG. 3) so that thethumb wheel can be moved by the operator. As the thumb wheel moves,thumb wheel gear 14, which is fixedly connected on the thumb wheelshaft, is made to rotate. This, in turn, moves pinion gear 15 whichcauses the rack 16 to move in the desired direction. Rack 16 is fixedlyconnected to the truck of member 17 thereby causing the truck to slidealong the tracks 40 and 41. Stop members 42' are positioned on thetracks such that the truck is caused to take a position between the stopmembers. Rollers 43 and 44 are mounted on shaft 45 and carried by thetruck of the movable support member 17. Rollers 43 and 44 come intocontact with the underside of leaf spring 18, as shown in FIG. 2. Thus,by rotation of the thumb wheel 13, the rollers 43 and 44 are caused tocontact the leaf spring at different points on the underside thereof.

FIG. 4 shows a schematic representation of the paper feed mechanismshowing the leaf spring 18. The movable support member 17 is shownpositioned some distance from the fixed support member stud 20. Roller22 is positioned at the end of the leaf spring 18 to come into contactwith, and support, the paper tray 24. The tray pivot point 51 also actsto support tray 24. A stack of paper 50 is shown positioned on the topsurface of paper tray 24.

FIG. 4 shows the preload arm 28 and the corner buckler arm 29. Thepreload pointer 30 is shown in FIG. 4 together with a reference pointer52 which is molded into the tray base 26. Feed roller 53 is shownpositioned above the stack of paper 50 to feed sheets from the stackover the corner buckler in the feed direction 54. Note that the preloadarm 28 is provided with an angled surface 55, which is a cammingsurface, to come into contact with a pin mounted in the machine in orderto move the preload arm 28 upwardly when the assembly is inserted intothe machine. The preload spring 27 is fastened to the preload arm 28 atone end, and to the paper tray base 26 at the other end.

In operation, for loading paper into the bin, the paper bin assembly 10is slideably moved from the machine so that paper can be placed on thepaper tray 24. The mechanism is designed so that the operator can adjustthe spring rate of leaf spring 18 while the assembly is removed from thebody of the machine. This is accomplished by rotating the thumb wheel 13until the preload pointer 30 and the reference pointer 52 are in linewith one another. Suppose, for example, that paper of a different sizeand/or density is loaded on the paper tray 24 relative to the paper usedduring the preceding load. In such a case, it will be necessary for theoperator to make the thumb wheel spring rate adjustment. The mechanismsare designed such that movement of the thumb wheel will move the leafspring support member 17, and thereby change the spring rate of leafspring 18. This causes the leaf spring 18 to exert a different force onthe underside of paper tray 24 thus causing the corner buckler to pressagainst the top sheet of the paper with a variable force. When thearrows 30 and 52 are in line, the corner buckler is designed to provideabout 0.5 pounds of force on the top sheet of the paper. When the paperbin assembly 10 is inserted into the machine, a pin bears against thecamming surface 55 of the preload arm 28 to lift the corner buckler outof contact with the top sheet of the paper stack. However, the preloadadjustment of the leaf spring ensures that as the feed roller 53 rotatesto a feeding position, it will bear against the top sheet of the paperwith approximately 0.5 pounds of normal force. Thus, the adjustment ofthe leaf spring movable support member 17, while the assembly 10 is outof operative position, enables the proper feed roll force when theassembly 10 is in operative position.

FIG. 5 is a schematic representation of the leaf spring 18 and showssupport member 17 at a first position, X minimum, and at a secondposition, X maximum. The spring rate of leaf spring 18 will vary from ahigh spring rate position at X maximum, to a low spring rate position atX minimum. As the spring rate varies, the amount of the deflection ofthe spring 18 also varies. That is, at the low spring rate position, theno-load deflection from the horizontal is greater than at the highspring rate position. FIG. 5 also shows that the support contact area ofleaf spring 18, provided by the movable support member 17, is offset ina vertical direction relative to the support provided by the fixedsupport 20. This offset is shown at 61.

FIG. 6 is a graphical representation of the variation in spring forcewith the number of sheets in the tray. One design objective is toprovide the same spring force when there are no sheets in the trayregardless of the position of the movable support member 17. A seconddesign objective is to provide a range of spring rate adjustment toaccommodate a range of different size and densities of paper. Thus, ifthere are 500 sheets of heavy paper in the bin, the movable supportmember will be moved toward the high spring rate position i.e., toward aspring constant of K max, and will provide a maximum force on theunderside of paper tray 24. If 500 sheets of low density small sizepaper are loaded in the bin, the movable support member 17 is movedtoward the low spring rate position i.e., toward a spring constant of Kmin causing the force exerted by the leaf spring to be considerablylower. As the sheets are fed from the bin, regardless of whether theyare heavy-weight paper or low-weight paper, it is desired to keep aconstant normal force between the top sheet in the bin and the feedroll. That is accomplished by the instant invention since the springforce decreases as sheets of paper are fed from the bin in a manner thatis related to the weight loss of paper as more and more sheets are fedout of the bin. Finally, at zero sheets of paper, the spring force isequal to that portion of the weight of the paper tray 24 carried by thespring (about 0.6 pounds in the preferred embodiment), together with thedesired 0.5 pounds of normal force exerted by the feed roll 53 againstthe unloaded tray 24.

FIG. 7 shows the spring force exerted by leaf spring 18 over a range ofpositions of the movable support member 17 with the number of sheets inthe bin equal to zero, and with the number of sheets equal to 500. It isa design objective to keep the spring force as linear as possible forthe condition in which the number of sheets in the bin is equal to zeroand thereby keep the desired 0.5 pounds force as the number of sheetsapproach zero, regardless of the position of member 17. When the numberof sheets equals 500, the shape of the spring-force curve is notsignificant since the truck position is adjusted by the thumb wheel toget the desired 0.5 pounds of force for the particular size and densityof paper in the bin.

The lift force the spring 18 must exert is defined by the followingequation

    F(n)=m * n * Wp+Wt+Fc

where:

m is the portion of the paper weight carried by the spring

n is the number of sheets

Wp is the weight of a single sheet

Wt is the portion of the metal support tray weight carried by the leafspring

Fc is the required contact force of the sheets against the feed roller

Variables m, Wt and Fc are constant. The number of sheets vary from 500to zero as the sheets are fed. The weight of a single sheet depends onthe size and density of the paper. As previously noted, FIG. 6 shows howthe force exerted by the spring 18 varies with the number of sheets inthe tray. The spring rate must allow for an adjustment in spring forcewhen the tray is fully loaded depending on the size and weight of thepaper in the tray. Also, the spring force with zero sheets in the traymust be the same regardless of spring rate adjustment, and the springforce must vary linearly as the number of sheets decrease.

While the invention has been described with reference to a paper binholding 500 sheets, and a desired normal force of 0.5 pounds between thefeed roll and the paper, obviously the principals of this invention canbe applied to a bin with a greater, or lesser, number of sheets of paperand a different normal force.

While the invention has been shown and described with reference to aparticular embodiment thereof, it will be understood by those skilled inthe art that changes in form and details may be made therein withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A sheet holding mechanism for use in a processingmachine, such as a copier or printer, comprising:bin assembly means forholding a stack of print-receiving material; a movable tray locatedwithin said bin assembly means for receiving said stack; sheet feedingmeans for moving the top sheet from said stack into said machine; leafspring means located within said bin assembly means for applying a forceto said movable tray to lift said tray to a position at which the topsheet on said tray is in a correct position for being fed into saidmachine by said sheet feeding means; and movable support means for saidleaf spring means for moving in a first dimension to adjust the springconstant of said leaf spring means to provide a constant normal forcebetween said top sheet and said sheet feeding means regardless of thesize and density of sheets on said movable tray.
 2. The sheet holdingmechanism of claim 1 further including:a fixed support means for saidleaf spring means; an offset in a second dimension between the contactareas with said leaf spring means of said fixed support means and saidmovable support means to provide a constant force on said tray underno-paper-load conditions regardless of the location of said movablesupport means.
 3. The sheet holding mechanism of claim 1 furtherincluding a preload mechanism for enabling the machine operator toadjust the spring constant of said leaf spring means when said binassembly means is removed from operative position within said machine.4. The sheet holding mechanism of claim 3 wherein said preload mechanismincludes:a thumb wheel means whereby an operator can adjust said springconstant; gear means operated by said thumb wheel means for moving saidmovable support means; a movable preload arm; a preload spring forbiasing said preload arm in a clockwise direction; a movable cornerbuckler arm on which a corner buckler is mounted for movement with saidpreload arm in said clockwise direction whereby said corner buckler isbiased against the top sheet in said stack when said bin assembly meansis removed from operative position within said machine; a pointermounted in said movable corner buckler arm; and a reference mark locatedon said bin assembly means whereby rotation of said thumb wheel enablesthe operator to move said pointer in line with said reference mark, thusenabling the adjustment of spring constant in accordance with the sizeand density of the paper load.